#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ld = long double;
using db = double;
using str = string;  // yay python!

using pi = pair<int, int>;
using pl = pair<ll, ll>;
using pd = pair<db, db>;

using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>;
using vs = vector<str>;
using vpi = vector<pi>;
using vpl = vector<pl>;
using vpd = vector<pd>;

#define tcT template <class T
#define tcTU tcT, class U
// ^ lol this makes everything look weird but I'll try it
tcT > using V = vector<T>;
tcT, size_t SZ > using AR = array<T, SZ>;
tcT > using PR = pair<T, T>;

// pairs
#define mp make_pair
#define f first
#define s second

// vectors
// oops size(x), rbegin(x), rend(x) need C++17
#define sz(x) int((x).size())
#define bg(x) begin(x)
#define all(x) bg(x), end(x)
#define rall(x) x.rbegin(), x.rend()
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pb push_back
#define eb emplace_back
#define pf push_front

#define lb lower_bound
#define ub upper_bound
tcT > int lwb(V<T>& a, const T& b) { return int(lb(all(a), b) - bg(a)); }

// loops
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define F0R(i, a) FOR(i, 0, a)
#define ROF(i, a, b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i, a) ROF(i, 0, a)
#define trav(a, x) for (auto& a : x)

const int MOD = 1e9 + 7;  // 998244353;
const int MX = 2e5 + 5;
const ll INF = 1e18;  // not too close to LLONG_MAX
const ld PI = acos((ld)-1);
const int dx[4] = {1, 0, -1, 0},
          dy[4] = {0, 1, 0, -1};  // for every grid problem!!
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
template <class T>
using pqg = priority_queue<T, vector<T>, greater<T>>;

// bitwise ops
// also see https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
constexpr int pct(int x) { return __builtin_popcount(x); }  // # of bits set
constexpr int bits(int x) {  // assert(x >= 0); // make C++11 compatible until
                             // USACO updates ...
  return x == 0 ? 0 : 31 - __builtin_clz(x);
}  // floor(log2(x))
constexpr int p2(int x) { return 1 << x; }
constexpr int msk2(int x) { return p2(x) - 1; }

ll cdiv(ll a, ll b) {
  return a / b + ((a ^ b) > 0 && a % b);
}  // divide a by b rounded up
ll fdiv(ll a, ll b) {
  return a / b - ((a ^ b) < 0 && a % b);
}  // divide a by b rounded down

tcT > bool ckmin(T& a, const T& b) {
  return b < a ? a = b, 1 : 0;
}  // set a = min(a,b)
tcT > bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }

tcTU > T fstTrue(T lo, T hi, U f) {
  hi++;
  assert(lo <= hi);  // assuming f is increasing
  while (lo < hi) {  // find first index such that f is true
    T mid = lo + (hi - lo) / 2;
    f(mid) ? hi = mid : lo = mid + 1;
  }
  return lo;
}
tcTU > T lstTrue(T lo, T hi, U f) {
  lo--;
  assert(lo <= hi);  // assuming f is decreasing
  while (lo < hi) {  // find first index such that f is true
    T mid = lo + (hi - lo + 1) / 2;
    f(mid) ? lo = mid : hi = mid - 1;
  }
  return lo;
}
tcT > void remDup(vector<T>& v) {  // sort and remove duplicates
  sort(all(v));
  v.erase(unique(all(v)), end(v));
}
tcTU > void erase(T& t, const U& u) {  // don't erase
  auto it = t.find(u);
  assert(it != end(t));
  t.erase(it);
}  // element that doesn't exist from (multi)set

// INPUT
#define tcTUU tcT, class... U
tcT > void re(complex<T>& c);
tcTU > void re(pair<T, U>& p);
tcT > void re(V<T>& v);
tcT, size_t SZ > void re(AR<T, SZ>& a);

tcT > void re(T& x) { cin >> x; }
void re(db& d) {
  str t;
  re(t);
  d = stod(t);
}
void re(ld& d) {
  str t;
  re(t);
  d = stold(t);
}
tcTUU > void re(T& t, U&... u) {
  re(t);
  re(u...);
}

tcT > void re(complex<T>& c) {
  T a, b;
  re(a, b);
  c = {a, b};
}
tcTU > void re(pair<T, U>& p) { re(p.f, p.s); }
tcT > void re(V<T>& x) { trav(a, x) re(a); }
tcT, size_t SZ > void re(AR<T, SZ>& x) { trav(a, x) re(a); }
tcT > void rv(int n, V<T>& x) {
  x.rsz(n);
  re(x);
}

// TO_STRING
#define ts to_string
str ts(char c) { return str(1, c); }
str ts(const char* s) { return (str)s; }
str ts(str s) { return s; }
str ts(bool b) {
#ifdef LOCAL
  return b ? "true" : "false";
#else
  return ts((int)b);
#endif
}
tcT > str ts(complex<T> c) {
  stringstream ss;
  ss << c;
  return ss.str();
}
str ts(V<bool> v) {
  str res = "{";
  F0R(i, sz(v)) res += char('0' + v[i]);
  res += "}";
  return res;
}
template <size_t SZ>
str ts(bitset<SZ> b) {
  str res = "";
  F0R(i, SZ) res += char('0' + b[i]);
  return res;
}
tcTU > str ts(pair<T, U> p);
tcT > str ts(T v) {  // containers with begin(), end()
#ifdef LOCAL
  bool fst = 1;
  str res = "{";
  for (const auto& x : v) {
    if (!fst) res += ", ";
    fst = 0;
    res += ts(x);
  }
  res += "}";
  return res;
#else
  bool fst = 1;
  str res = "";
  for (const auto& x : v) {
    if (!fst) res += " ";
    fst = 0;
    res += ts(x);
  }
  return res;

#endif
}
tcTU > str ts(pair<T, U> p) {
#ifdef LOCAL
  return "(" + ts(p.f) + ", " + ts(p.s) + ")";
#else
  return ts(p.f) + " " + ts(p.s);
#endif
}

// OUTPUT
tcT > void pr(T x) { cout << ts(x); }
tcTUU > void pr(const T& t, const U&... u) {
  pr(t);
  pr(u...);
}
void ps() { pr("\n"); }  // print w/ spaces
tcTUU > void ps(const T& t, const U&... u) {
  pr(t);
  if (sizeof...(u)) pr(" ");
  ps(u...);
}

// DEBUG
void DBG() { cerr << "]" << endl; }
tcTUU > void DBG(const T& t, const U&... u) {
  cerr << ts(t);
  if (sizeof...(u)) cerr << ", ";
  DBG(u...);
}
#ifdef LOCAL  // compile with -DLOCAL, chk -> fake assert
#define dbg(...)                                                     \
  cerr << "Line(" << __LINE__ << ") -> [" << #__VA_ARGS__ << "]: [", \
      DBG(__VA_ARGS__)
#define chk(...)                                                    \
  if (!(__VA_ARGS__))                                               \
    cerr << "Line(" << __LINE__ << ") -> function(" << __FUNCTION__ \
         << ") -> CHK FAILED: (" << #__VA_ARGS__ << ")"             \
         << "\n",                                                   \
        exit(0);
#else
#define dbg(...) 0
#define chk(...) 0
#endif

void setPrec() { cout << fixed << setprecision(15); }
void unsyncIO() { cin.tie(0)->sync_with_stdio(0); }
// FILE I/O
void setIn(str s) { freopen(s.c_str(), "r", stdin); }
void setOut(str s) { freopen(s.c_str(), "w", stdout); }
void setIO(str s = "") {
  unsyncIO();
  setPrec();
  // cin.exceptions(cin.failbit);
  // throws exception when do smth illegal
  // ex. try to read letter into int
  if (sz(s)) setIn(s + ".in"), setOut(s + ".out");  // for USACO
}

const int BIG = 3000000;
vi stor[2 * BIG];
int N;
vi v;

int dif(int x) { return v[x] - x + N; }  // add N so difference is non-negative

int main() {
  setIO();
  re(N);
  v.resize(N);
  re(v);
  vi mn, mx;
  int maxL = -1;
  vpi ans;
  for (int j = 0; j < v.size(); ++j) {
    while (sz(mn) && v[mn.bk] > v[j]) {
      stor[dif(mn.bk)].pop_back();
      mn.pop_back();
    }
    while (sz(mx) && v[mx.bk] < v[j]) mx.pop_back();
    int ind = dif(j);
    if (sz(stor[ind])) {
      int x = stor[ind].bk;
      if ((!sz(mx) || mx.bk < x) && x > maxL) {
        maxL = x;
        ans.pb({x, j});
      }
    }
    mn.pb(j);
    mx.pb(j);
    stor[ind].pb(j);
  }
  ps(sz(ans));
  trav(t, ans) ps(t.f + 1, t.s + 1);
}
